The adblocker check looks at the height/width attributes of the elements containing the puppy games adverts. If these are 'auto' it assumes that the ads are being suppressed. It's all in the page source.

I saw the same thing despite not having an ad blocker. Firefox 18.0.2, Windows 7. It wasn't a big deal, just a little "umm..." moment. I don't see it now, and I do see the featured project and latest featured stuff on the side (although nothing in the Picture of the Day, but that might be a separate issue).

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